1. Field of the Invention
The invention relates to an apparatus for and a method of controlling a variable valve actuation system capable of changing a valve characteristic of engine valves by using an actuator whose movement range is between a first end and a second end at each of which the movement thereof is mechanically stopped.
2. Description of Related Art
As a system installed for an internal combustion engine that is mounted in a vehicle or the like, there have been commercialized variable valve actuation systems that change a valve characteristic of engine valves (intake and exhaust valves). As such a variable valve actuation system, there is known a system capable of changing the angle of action of the engine valves.
FIG. 8 shows an example of a variable valve actuation system capable of changing the angle of action of valves. This variable valve actuation system includes an actuator 103 that is made up of an electric motor 100 and a rotation/linear motion conversion mechanism 104 that converts rotation of the electric motor 100 into linear motion of a control shaft 101. On the control shaft 101, there is disposed a variable angle-of-action mechanism 102 that expands or reduces the angle of action of engine valves according to linear motion of the shaft 101.
Incidentally, the range of the linear motion of the control shaft 101 is mechanically restricted by stoppers 105 and 106. Using the stoppers 105 and 106, the movement range of the actuator 103 is restricted to a range between a high end and a low end at which the movement of the control shaft 101 is restricted mechanically by the stoppers 105 and 106, respectively.
The actuator 103 is controlled by an electronic control unit 108. The electronic control unit 108 receives a detection signal from a movement amount sensor 107 that detects the amount of movement of the actuator 103.
At the time of start of the valve angle-of-action control, the electronic control unit 108 drives the actuator 103 until the high end or the low end is reached, and then learns the position at which the movement is stopped, as a reference movement position. Then, the electronic control unit 108 determines an actual movement position of the actuator 103, that is, determines the actual angle of action of the engine valves, based on the amount of movement of the actuation 103 from the reference movement position. Because of this mechanism, it is possible to control the actual angle of action of the engine valves to a targeted angle of action without a need to directly detect the actual angle of action of the engine valves or the actual movement position of the actuator 103.
In some cases, however, the movement of the actuator 103 becomes fixed because of entrance of a foreign object into an engaging portion or the like. As a technology for determining whether or not the actuator 103 is having such a movement fixation, there are known technologies described in Japanese Patent Application Publication No. 2008-157088 (JP-A-2008-157088), Japanese Patent Application Publication No. 2008-286172 (JP-A-2008-286172), and Japanese Patent Application Publication No. 2009-299543 (JP-A-2009-299543).
In JP-A-2008-157088, the amount of movement of the actuator 103 when the actuator 103 is driven from the low end to the high end is measured, and if the measured value of the amount of movement is greatly deviated from a designed value thereof, it is determined that the aforementioned fixation is present.
Besides, in JP-A-2008-286172, the actuator 103 is driven to the high end and to the low end, and the positions thereof are learned. Then, if the distance between the high end and the low end that is determined from results of the learning is less than a designed value, it is determined that there has been a false learning about the high end or the low end due to fixation or the like.
Furthermore, in JP-A-2009-299543, it is determined that there is a possibility of presence of fixation when it is found for the first time that the actual movement position of the actuator 103 has not changed in response to a movement command that is output from the electronic control unit 108 to the actuator 103. Then, if it is found again that there is no change in the actual movement position of the actuator 103 in response to the movement command after the actuator 103 has been driven to the low end and the reference movement position has been re-learned, the determination that the fixation is present is established.
If the movement position of the actuator 103 is known, it is possible to immediately determine that fixation is present based on a finding that at an movement position other than the high end and the low end, the actuator 103 does not operate in response to the movement command from the electronic control unit 108. However, in the case where the movement position of the actuator 103 is not known, such as the case where the reference movement position has not been learned yet or the case where the power supply to the actuator 103 has been cut off, if the actuator 103 fails to operate, it cannot be determined whether the failure to operate is a result of fixation or a result of the arrival at the high end or the low end.
The above-described related-art fixation determination methods may be able to check whether or not fixation has occurred, but needs many procedure steps in order to complete the checking. Therefore, the related-art methods are not able to promptly check the presence or absence of fixation in a situation as mentioned above. For example, in JP-A-2008-157088 and JP-A-2008-286172, in order to perform the checking about fixation, it is necessary to drive the actuator 103 both to the high end and to the low end. In JP-A-2009-299543, in order to establish the determination that fixation is present, it is necessary to perform the re-learning of the reference movement position by driving the actuator 103 to the low end. Thus, all the related-art technologies require considerable amounts of time in order to determine the presence or absence of fixation. Besides, particularly in JP-A-2008-157088 and JP-A-2008-286172, the false learning of the reference movement position due to fixation is inevitable, and the variable control of the angle of action of valves is performed with a false recognition of the movement position until the presence of fixation is determined.
Incidentally, these problems can occur in any control apparatus for a variable valve actuation system in substantially the same manner as described above, as long as the control apparatus controls the variable valve actuation system by performing the learning of the reference movement position at the first end or the second end at each of which the movement of the actuator is mechanically stopped and then checking the movement position of the actuator based on the amount of movement thereof from the reference movement position.